Inspect the FICM wire harness at the passenger side of the alternator. The harness and wires get cut, and sometimes short to ground, by contact with the sharp corner of the FICM bracket.
The harness is tied down with a zip tie, cut the zip tie and look carefully at the under side. Insulate with a piece of heater hose.
This is a common problem for the LLY engine.
Everyone that has a LLY should check this now!
Chevy 04.5 LLY, 2X, shell, XDR, MikeL Heavy duty up-grade, 6spd, TransGo, deep pan, de-badged, 65 Gallon replacement Aero tank, LBZ-mp, Kennedy pump, shimmed, Pre-fuel filter, tow mirrors, BU cam, gauges, GPS, Sirius, bags, custom grille, fender vents, HD trans cooler- Curt front hitch, footwell lights, load lights, Studs, head gaskets.